Exemplary embodiment of the invention relate to a method for clarifying a flowable starting product with a separator with a rotatable drum having a feed, at least one liquid discharge for continuously discharging at least one clarified liquid phase, and discontinuously openable solid-discharge openings for continuously discharging the solid phase.
German patent document DE 32 28 074 A1 discloses a method allowing in an advantageous way control of a continuously evacuating clarifying separator with a drum. A product parameter—here the degree of turbidity of a clear phase running out from the drum—is determined and used to monitor the evacuation of the solids chamber of the drum. In this case, the solid phase is continuously evacuated. If the turbidity or the degree of turbidity in the clear phase becomes too high, a return of the clear phase into the drum takes place.
It is additionally also known to use a clarifying separator for clarifying liquids, in particular beverages, in which the solids are discontinuously evacuated with the aid of a piston slide valve for opening and closing discharge openings when the degree of turbidity measured by the photocell exceeds a certain limit value.
This method has also proven itself, such as for example in the clarification of beverages comprising turbid substances. It is problematic, however, that, when measuring the degree of turbidity of the clear phase, limit values have to be prescribed, the reaching of which often means that there is already an undesirably high proportion of turbid substances in the beverage when the evacuation of the solids takes place. This is so because it is only with difficulty that an incipient turbidity of the clear phase can be precisely determined by sensors.
An exemplary embodiment of the invention is directed to a method for clarifying a flowable starting product (AP) with a—self-evacuating—separator with a rotatable drum with a feed and at least one liquid discharge for continuously discharging at least one clarified liquid phase—a clear phase—and with discontinuously openable solid-discharge openings for discontinuously discharging the solid phase. The method involves the following steps: a. setting or determining a starting time; b. repeatedly determining at least one actual value of a product parameter of the clear phase (KP) drawn off from the drum; c. determining the calibrating time interval from the starting point until the time at which the product-parameter actual value or the difference quotient of the determined product-parameter actual values and the respective time intervals between the measurements reaches or exceeds a limit value, in particular a product-parameter limit value; d. preferably initiating a solid discharge as a consequence of reaching or exceeding the limit value, in particular the product-parameter limit value; e. determining and setting an operating time interval t(B) by means of the determined calibrating time interval t(K), the operating time interval t(B) being less than or equal to or greater than the determined calibrating time interval t(K); and f. initiating at least one or more solid discharges each time the set operating time interval t(B) has elapsed.
When starting up the drum, the time of step a. may be the starting time or the time of the beginning of the product feed into the drum. Otherwise, the time of the last solid evacuation is preferably used.
In this case, the calibrating time period may also be determined indirectly from the time of the solid evacuation or as the time period between two solid evacuations. The further solid evacuation of step d. is to this extent merely the consequence of the deviation of the product parameter from the setpoint value and is time-dependent on this event. In particular according to the measuring method of International patent document WO 2008/058340 A1, establishing when a value is below a limit value may be a suitable method with which the turbidity in a separate line to the outlet of the drum and/or in a bypass line or the like is measured.
The determination of the actual value of the product parameter may be performed, for example, by the quasi-continuous determination of measured values. It is however also possible to determine just some measured values at periodic times of somewhat greater intervals. As a result, the measured values can be used to determine a measuring curve, which allows a statement to be made concerning the change in the product parameter.
The initiation of the second solid discharge preferably ends the calibrating interval. The clear phase carried out in the calibrating interval corresponds qualitatively to the clear phase according to the prior art, since a change in the parameter in a significant way has already commenced. Therefore, in fact no qualitative change in comparison with the prior art is achieved during the calibrating interval. This improvement is made possible however by steps e) and f) now allowing other prescribed time settings to be made than is possible on the basis of the measurements alone, which is explained still more specifically further below on the basis of examples.
The determination and setting of the operating time interval may be performed by various mathematical operations. For instance, a preset time interval may be subtracted from the determined calibrating time interval. An analysis of the measuring curve, that is to say the variation over time of the measured values, over the calibrating time interval may also be performed by the evaluation unit or the end user and the setting of the operating time interval may be performed in dependence on this evaluation. Not least, a factorizing of the calibrating interval is also possible, the factor, which is multiplied by the calibrating time interval, preferably being less than 1. After the set operating interval has passed, a solid discharge is initiated. The solid discharge is consequently time-controlled and not initiated in dependence on a measurement.
In such a way—with the assumption of properties of the incoming product remaining the same, at least to the greatest extent—a solid evacuation may already take place when the change is not yet measurable or is just measurable. If the product parameter is, for example, the turbidity content of a clear phase, an increase in the turbidity or the degree of turbidity in the clear phase to a limit value is accepted once in the determination of the calibrating time interval. Several further evacuations are then performed in a time-controlled manner such that this limit value is not reached in the first place, and the turbidity preferably lies well below it. In such a way, the turbidity content of the clear phase drawn off is altogether reduced and the quality of the clear phase drawn off is improved overall. Only after several time-controlled solid evacuations is a calibration then performed again by measurement, in order to check whether the product properties of the incoming product to be processed have changed, so that an adaptation of the operating time interval is necessary. As a result of the shortened operating time interval in comparison with the calibrating time interval, the solids collecting chamber of the separator is therefore preferably evacuated earlier, and the clear phase has product parameters—here in particular the degree of turbidity—that remain virtually the same over the course of the operating time interval.
The aforementioned steps of the method serve for controlling the operation of a separator. However, the individual method steps do not necessarily have to be carried out in a structural unit of the separator, they may alternatively be carried out by external devices (measuring devices, sensors, evaluation unit).
It may be required to adapt the aforementioned operating interval from time to time to changes of the properties of the clear phase as a consequence of changes in the properties of the incoming product—in particular if it is a natural product such as a cider or must to be clarified or a fruit or vegetable juice or a beer or the like. Such a change in the properties may occur, for example, during the processing of natural products containing turbid substances that have previously been stored in a tank. In this case there forms a sediment with greater amounts of turbid substances. If liquid is fed to the separator as a starting product from the region of the sediment, the content of solids becomes higher and the solids must be evacuated more often. It is therefore of advantage if, after a predetermined number of passages of operating time intervals, a renewed run-through of steps a)-d) takes place and the operating interval is adapted to the current measurement.
It is optionally also advisable if parameters of the starting product are included in the method according to the invention. For instance, a determination of the volumetric feed flow or a product parameter of the starting product fed to the separator may be performed and a renewed run-through of steps a-f) take place if the volumetric flow changes or the product parameter changes beyond a limit value.
The product parameter of the clear phase may be not only the degree of turbidity but also some other measurable parameter, such as the viscosity and/or the conductivity. Sensors or measuring devices with correspondingly designed sensors for determining these parameters can be attached comparatively easily to the separator at the corresponding outlets.
It is of advantage if the operating time interval is chosen in such a way that, within the operating time interval, the product parameter of the clear phase directly before the evacuation deviates by less than 50%, preferably less than 20%, from the product parameter of the clear phase directly after the solid discharge. If for example the degree of turbidity was chosen as the parameter, it has been possible until now—as also emerges, inter alia, from FIG. 2—for just one solid discharge or one solid evacuation to take place if the degree of turbidity of the clear phase toward the end of the time interval in which the solid matter is collected in the separator reached a multiple of the degree of turbidity of the clear phase directly after the evacuation. This excessive increase in the degree of turbidity of the clear phase shortly before the evacuation is prevented by the novel setting of the operating interval.
Ideally, the operating time interval is less than the calibrating time interval by at least 5%, preferably at least 10%.
As is usual with a discontinuous solid discharge, the solid discharge preferably takes place through discharge openings in the manner of nozzles, which can be closed and opened by a piston slide valve. This has the advantage in particular that the opening state of the discharge nozzles is precisely controllable.
The determination of the calibrating time interval and the operating interval and the setting of the operating time interval are preferably performed using an evaluation unit formed as a software routine of a control computer that is connected to the sensors and allows an activation of the actuating mechanism of the piston slide valve in the drum.
An exemplary embodiment of the invention is directed to a method for clarifying a flowable starting product (AP) with a centrifuge, in particular a separator with a rotatable drum with a feed and at least one liquid discharge for continuously discharging at least one clarified liquid phase—a clear phase—and with discontinuously openable solid-discharge openings for discontinuously discharging the solid phase, which has at least the following steps: a) preferably setting or determining a starting time; b) repeatedly determining/measuring at least one actual value of a product parameter of the clear phase (KP) drawn off from the drum; c) determining and evaluating the difference quotient from the determined product parameters and the respective time intervals between the measurements; and d) initiating a solid discharge as a consequence of the evaluation in step c).
After step d), steps a) to d) preferably start anew.
According to the alternative solution of features c) and d) of the embodiments, the increase in the product parameter, in particular the increase in the turbidity, is not directly detected, but instead the difference quotient from the measured values of the product parameter and the time intervals between the measurements is determined and evaluated.
Dependent on this evaluation, an evacuation is possibly initiated. Only if the behavior of this difference quotient (that is to say the variation of the numerical differentiation of the product parameter function, known only as an approximation in the form of discrete measured values, in dependence on time) deviates from a prescribed and prestored behavior, that is to say in particular if the difference quotient (or the first derivative) for example reaches or falls below or exceeds a prescribed limit value one or more times, is the evacuation initiated. According to claim 1, steps e) and f) are then run through, i.e. fixed times for one or more further evacuation intervals are defined. According to this embodiment, it is however also conceivable to run through steps a) to d) of this claim anew.
This procedure is considered more specifically on the basis of the example of the product parameter “degree of turbidity” in dependence on time. The degree of turbidity is determined in time intervals by a measurement. Then, the difference quotients from the degree of turbidity and the time interval between the respective measurements are determined and evaluated. A (numerical) detection of a change, for example an increase, in the difference quotient allows a conclusion to be made at a relatively early time, or advantageously detection of a commencing clearer or faster increase in the turbidity. In this situation, an additional solid evacuation is advisable. Also with this procedure, the risk of belated evacuations can consequently be prevented.
The method of this embodiment also allows further conclusions to be made. For instance, it may be that it is found in the evaluation of the difference quotient that it changes only very little over a relatively long time period. This may have the following cause. In the case of a very slow increase in the solid content in the separator drum, there is the risk of the disk stack in the separator drum gradually being covered with solids. This is the reason for the demonstrated continuous increase in the turbidity or the degree of turbidity (“sawtooth effect”) and the dynamic limit value in the course of a day. In this case, it is conceivable that solids have already been discharged repeatedly, although the proportion of solids is in fact not yet as high as it should be in the case of an evacuation. It is consequently advisable to carry out an evacuation at an earlier time than intended. In this situation, it appears to be advantageous to define the limit value from the behavior of the derivative of the turbidity function in dependence on time. This is so because an evaluation of the derivative function makes it possible to distinguish the very slow increase from other increases.
Other effects that may influence the variation in the increase in the proportion of solids in the separator drum are a possibly necessary throttling of the feed rate, a possibly necessary flushing of the shroud or a pre-filling of a hydrostop system. Also in these situations, too many solids could already be entrained into the liquid outlet for the liquid phase. Also in this situation, the alternative method provides an easy remedy. This is so because an evaluation of the derivative function makes it possible to detect the situations described.
It is optionally also conceivable in the event of a decrease in the turbidity or in the event of a turbidity remaining the same to carry out a renewed measurement and to discard values previously stored. In this way, inadmissible evacuations that could for example otherwise occur in the event of changes in pressure surges or changes in through-flows in the system can be prevented.